As is known to those skilled in the art, it is quite difficult to prepare solid, high molecular weight homopolymers of the bis(hydrocarbyl) vinylphosphonates such as bis(beta-chloroethyl) vinylphosphonate. It is also difficult to prepare high molecular weight copolymers of these vinylphosphonates wherein they are present in proportions which substantially exceed about 50%, by weight. The preparation of such homo- or copolymers of these vinylphosphonates is, of course, highly desirable inasmuch as they are characterized by a high degree of fire retardancy; the latter property being particularly useful for the various reasons which will be set forth hereinbelow.
Thus, many thermoplastic polymers such, for example,
AS THE HOMO- AND THE COPOLYMERS OF METHYL METHACRYLATE, POLYOLEFINS, POLYSTYRENE AND ACRYLONITRILE-BUTADIENE-STYRENE RESINS ARE HARD AND, IN MANY INSTANCES, OPTICALLY CLEAR MATERIALS WHICH ARE WIDELY UTILIZED FOR THE PREPARATION OF A BROAD RANGE OF CONSUMER AND INDUSTRIAL ARTICLES. As normally prepared, these thermoplastic polymers will ignite and continue to burn upon exposure to flames or high temperatures. However, in many instances, particulatly where they are being considered for use in building interiors or in applications requiring their prolonged exposure to high temperatures, it is highly desirable that such polymers should display fire or flame retardant properties so that they may either meet the standards set by various building codes or so that they may be safely employed in place of more costly materials.
Prior attempts to provide fire retardant, thermoplastic polymer compositions have involved the use of a variety of extraneous additives such, for example, as antimony oxides, halogentated paraffins, halogenated hydrocarbons and low molecular weight phosphate esters. However, the effective utilization of these and other additives has ordinarily required their presence in rather high concentrations which adversely affected the physical properties of the treated polymers. Thus, the inherent hardness and, in some instances, the clarity of the thermoplastic polymers were particularly prone to deterioration in the presence of the high concentrations of these additives which were necessary in order to achieve a self-extinguishing polymer composition.
It is, therefore, the prime object of this invention to provide a means for preparing solid, high molecular weight copolymers capable of containing as much as about 98%, by weight, of one or more bis(hydrocarbyl) vinylphosphonates. It is a further object of this invention to utilize such copolymers either per se as fire retardant materials or as polymeric additives which may be blended with burning thermoplastic polymers, i.e. with thermoplastic polymers which will continue to burn upon being ignited, in order to enhance their fire retardant characteristics without adversely affecting the inherent physical properties such as hardness and, in some instances, the clarity of the thus modified polymers. Various other objects and advantages of this invention will be apparent from the disclosure thereof which follows hereinafter.